New chromosome types in Drosophila are being synthesized belonging to the general category of compound chromosomes. Previous work with the second chromosome has yielded a complete compound second chromosome. This has a number of interesting properties, one of which is a very low transmissibility through the male line. The chromosome has been taken apart and the centromere region changed in several ways. Transmissibility is improved when the centromere region from a 2-3 translocation replaces that of the second already present. With this modification, the compound is being reconstructed to form the basis for a similar compound of the third chromosome. These compounds are currently being exploited in a number of experiments where they are uniquely suitable because of their composition of two homologues. BIBLIOGRAPHIC REFERENCES: 1976 Novitski, E. and D. childress. Compound Chromosomes Involving the X and the Y Chromosomes, from The Biology and Genetics of Drosophila, Vol. I, M. Ashburner and E. Novitski, Eds., Academic Press, London. 1976 Novitski, E. The Construction of an Entire Compound Two Chromosome, Appendix from The Biology and Genetics of Drosophila, Vol. I,M. Ashburner and E. Novitski, Eds., Academic Press, London.